Now to start off in the deep, there are some things which will allow you to handle the basics. And these things are all explained in the set of guides righ here in the sidebar. Going through these will allow you to get some basic dimensions and guides on handling anatomy and drawing methods.

To explain what they will serve you to do would be that they contain visual references, dimensions and some process explanation on how to get to drawing a pony.

Now what you also want to consider is taking references, those will help you out a lot with figuring out dimensions, because you can cross reference to what you see in your reference to what you see in your drawing. For example look at this guide on how to do something with a reference.

What I would advice is getting down on the basic anatomy of a pony, there are some differences I'll cover a bit further.

Now for drawing technique, did you use an undersketch? If you haven't let me rapidly explain the idea. The undersketch is the messy part where you rapidly sketch, using basic shapes, skeletons and other necessary lines to make the rough shape of what you want to do. You would like to have the undersketch to be properly made before lining the image, because if an error is made in the undersketch it will continue in the "inking". Now this is by no means the excuse that the undersketch has to be perfect, in fact it is messy, very messy. But it allows you to see if what you made works.

Well with that said, let me give you some things I notice with what you made which I can help with.

The basic used dimensions which you'll find are commonly used are 3-2-3. The head is 3/2rd the size of the body circles, while the legs are about as high as the head is big. If you look at your drawing, you made it closer to a horse and further away from the anatomy they handle in the show.

The wing is very square, look at references of pegasi to get a feel of how those look, You'll notice that the wings are sort of stretched egg shaped and maintain the curving nature of a pony.

The legs are rather thin, its good that the hoof sizes remain the same back and front, because that is how it's usually done. I would advice taking guides with skeletons explained in them like here in this guide (3rd image from the top).

Now little minor things which can be forgotten easily, the eye is missing light spots, it usually results in a hollow unfocused look without them. Oh and uh, no tail hehe

Well I do hope this helps! If not, I tried.

Feel free to follow up with questions or things which are unclear or anything.